we will randomize users of the app that opt-in to receive messages to one of the possible conditions:
- standard reminder (Control)
- message about sunk costs (Treatment1)
- message with info about other users' steps (Treatment2)
- messages about their own number of steps in the prev day (Treatment3)
All the subjects will receive the standard reminder for two weeks, then will be allocated to the control or one of the treatments. these will last 1 week for half of the sample, 3 weeks for the other, and then go back to the standard message.
We will collect the number of daily steps for the period just after the intervention (weeks) and some months after, according to data availability.